One of the principal mechanisms by which cellular regulation is effected is through the transduction of extracellular signals across the membrane that in turn modulate biochemical pathways within the cell. Protein phosphorylation represents one course by which intracellular signals are propagated from molecule to molecule resulting finally in a cellular response. These signal transduction cascades are highly regulated and often overlapping as evidenced by the existence of many protein kinases as well as protein phosphatases. It is currently believed that a number of disease states and/or disorders are a result of either aberrant expression or functional mutations in the molecular components of kinase cascades. Consequently, considerable attention has been devoted to the characterization of these proteins.
Nearly all cell surface receptors use one or more of the mitogen-activated protein kinase (MAP kinase) cascades during signal transduction. Three distinct subgroups of the MAP kinases have been identified and each of these consists of a specific module of downstream kinases. These subgroups consist of the extracellular signal-regulated protein kinase pathway (MAPK/ERK kinases), the Jun N-terminal kinase/Stress activated protein kinase pathway (JNK/SAPK kinases) and the p38 kinase pathway. The MAPK/ERK pathway is activated by signals emanating from growth factor stimulation while the p38 pathway is activated by high osmolarity, lipopolysacharides, tumor necrosis factor-.alpha., and interleukin-1 (Moriguchi et al., Adv. Pharmacol., 1996, 36, 121-137). The JNK/SAPK pathway was originally identified as an oncogene- and ultraviolet light-stimulated kinase pathway but is now known to be activated by growth factors, cytokines and T-cell costimulation (Moriguchi et al., Adv. Pharmacol., 1996, 36, 121-137; Su and Karin, Curr. Opin. Immunol., 1996, 8, 402-411).
MEKK5 (also known as mitogen-activated protein kinase kinase kinase 5, MEK kinase 5, MAP/ERK kinase kinase 5 and ASK1 or apoptosis signal-regulating kinase 1) is a dual specific serine/threonine kinase that functions to mediate cellular responses to mitogenic stimuli by activating both the JNK/SAPK and the p38 modules of MAP kinase cascades (Ichijo et al., Science, 1997, 275, 90-94; Wang et al., J. Biol. Chem., 1996, 271, 31607-31611). The protein is ubiquitously expressed with the highest expression in the heart, pancreas, testis and ovaries (Ichijo et al., Science, 1997, 275, 90-94).
It is currently believed that MEKK5 plays a critical role in the regulation of apoptosis or programmed cell death by interacting with other proteins in this cascade and by phosphorylating downstream targets such as MKK3 and SEK1. Consequently, MEKK5 activity has been associated with pathologic conditions such as inflammation and wound healing (Funato et al., Lab. Invest., 1998, 78, 477-483; Nishitoh et al., Mol. Cell., 1998, 2, 389-395).
Recently it was demonstrated that the tumor necrosis factor .alpha.-induced activation and dimerization of MEKK5 is mediated by reactive oxygen species (ROS) (Gotoh and Cooper, J. Biol. Chem., 1998, 273, 17477-17482). Subsequently, it was shown that thioredoxin, a reduction/oxidation regulatory protein, associates with MEKK5 and inhibits MEKK5 kinase activity and MEKK5-dependent apoptosis (Saitoh et al., Embo. J., 1998, 17, 2596-2606).
MEKK5 also participates in another apoptosis related signaling cascade involving the modulation of transcription factors. MEKK5 was shown to be activated by the adapter protein, Daxx. This protein enhances Fas-induced apoptosis by activating the JNK/SAPK kinases culminating in the phosphorylation of transcription factors (Chang et al., Science, 1998, 281, 1860-1863).
Currently, there are no known therapeutic agents which effectively inhibit the synthesis of MEKK5 and to date, strategies aimed at modulating MEKK5 function have involved the use of antibodies, dominant negative and dominant active mutants of the protein. Consequently, there remains a long felt need for agents capable of effectively inhibiting MEKK5 function.
Antisense technology is emerging as an effective means for reducing the expression of specific gene products and may therefore prove to be uniquely useful in a number of therapeutic, diagnostic, and research applications for the modulation of MEKK5 expression.